Method 1 - Determine Workspace & Project OIDs from URL (Any User Permission)
Project and Work Item Object ID:
The URL of a Work Item contains the OID (Object ID) of the Project where the given Work Item is contained.
Navigate to the Detail Page of the CA Agile Central Work Item (User Stories, Tasks, Portfolio Items, Test Cases, Test Case Results, Defects, and Defect Suites)

In the above example, "2xxxxxxxx61" is the Project OID, while "51xxxxxxxx28" is the OID of the User Story being accessed. Note that the trailing 'd' is not part of the ObjectID. Letters 'd' or 'u' indicate current selection to scope down or up in the project hierarchy. For more information see this article:
What is the significance of a trailing d after an ObjectID in the URL?
Workspace Object ID
The Workspace OID may be copied from the URL when performing a Web Services API (WSAPI) query. This can be found with any query, though we will give an example below.
- Navigate to https://rally1.rallydev.com/slm/doc/webservice/ (Requires login to CA Agile Central)
- From the left-hand navigation, click Artifact
- Click the Query button and inspect the URL in the resulting window
In the above example, "2xxxxxxxx46" is the Workspace OID
Method 2 - Determine Workspace & Project OIDs from URL (Subscription or Workspace Administrator)
Both the Workspace and Project OIDs can be copied from the URL of their direct Detail Pages. Only administrators however have access to the Workspace and Project detail pages.
- Logged in as an administrator click Setup at the top-right (hammer and wrench icon)
- Click the Workspaces & Projects tab
- Click the Name of either a Workspace (top-level in tree) or Project to view the Detail Page

In the first above example "/workspace/5xxxxxxxx25" is the Workspace OID (From Workspace Detail Page)

In the second above example "/project/5xxxxxxxx09" is the Project OID (From Project Detail Page)
Method 3 - Use Custom Page and the Custom HTML App
Use the following article for steps on accessing workspace and project object IDs: